Image Guided Radiation Therapy
Image-guided radiation therapy (IGRT) is a process of using various imaging technologies to locate a tumor prior to turning the radiation beam on. Radiation oncologists use image-guided radiation therapy, or IGRT, to help better deliver the radiation to the cancer since tumors can move between treatments due to differences in organ filling or movements while breathing. All patients first undergo a CT scan as part of the planning process. The imaging information from the CT scan is then transmitted to a computer in the treatment room to allow doctors to compare the earlier image with the images taken just before treatment. During IGRT, your treatment team can compare these images to see if the treatment needs to be adjusted. This allows us to better target the cancer while avoiding nearby healthy tissue. IGRT is complementary to IMRT. IMRT is used to improve the radiation delivery precision and IGRT is used to improve the radiation delivery accuracy.
Similar to TomoTherapy® the Trilogy® radiation machine also offers state of the art image guidance capability with real time CT capability. Trilogy® also offers the capability of performing non-IMRT treatments especially for certain cancer types where IMRT is not the best way to treat the patient. In addition, trilogy allows a radiation oncologist to deliver the most precise delivery of radiation to small tumors within the brain or other parts of the body. This treatment is known as stereotactic radiosurgery or SRS. Among the technological innovations that come with the system is "respiratory gating," which tracks the position of a tumor in sync with a patient's breathing, turning the radiation off and on to compensate for motions of inhalation and exhalation. The technology enables a physician to choose exactly the right moment to target a tumor, allowing increases to radiation doses while protecting healthy tissues. Of equal importance, the Trilogy system can target with high specificity a tumor that lies problematically close to the spinal cord, optic nerves, brainstem, skull base and other critical organs. This unparalleled accuracy can lead not just to better outcomes but also to greater efficiencies, shorter hospital stays and reduced risk of complications.
In many ways Trilogy® and TomoTherapy® are interchangeable. Your radiation oncologist will discuss which type of machine is most appropriate for your type of cancer.
An example of an image acquisition of a cone-beam CT (CBCT) taken on the day of treatment on the Varian Trilogy® unit shows the CBCT (white) being digitally overlaid on the simulation CT scan used for treatment planning (grey). The patient is automatically moved to line up precisely with the position on the scan used for treatment planning. (courtesy of Varian)
A cone-beam CT (CBCT) on the left is taken on each day of treatment to precisely line up the treatment area (lung tumor encircled by the purple line) to the scan used for planning the treatment on the right.